Modern, powerful vehicle gearboxes usually comprise a main transmission group with a multi-stage basic gear and an upstream or downstream splitter group and/or a downstream range gear group. In a gearbox housing, they mainly comprise an input shaft as a first shaft and a central or main shaft as a second shaft, which can also be the output shaft, as well as one or more countershafts. The input and main shafts are essentially concentric with one another.
Having regard to the running properties and smooth running, such gearboxes can be designed with helical gearing, at least for the forward driving range. The axial forces from the helical gearing have to be taken up by an axial bearing and transmitted to the housing.
Gearboxes with the structure described can have one or more countershafts.
In gearboxes with power distribution between two countershafts, the main transmission group comprises two shafts arranged essentially one behind the other, one of which, namely either the input shaft or the main shaft of the main transmission, is mounted radially and axially fixed, while the respective other shaft is mounted floating laterally, i.e., able to move radially to allow the necessary load equalization. In this, care should be taken that an easy swivelling motion of the floating shaft is possible.
In gearboxes with two countershafts, the load equalization can preferably be designed such that the input shaft is mounted fixed on the housing, the countershafts are fixed on the housing and the main shaft is mounted floating in the gear wheels involved in the force flow.
The known variable-speed gearboxes for goods vehicles have a three- or four-speed main or basic transmission section and an upstream or downstream splitter transmission as an auxiliary transmission, which doubles the number of gear speeds of the main transmission since it splits the transmission ratio steps of the main transmission. A range-change transmission downstream from the main transmission extends the ratio range of the main transmission. The range-change transmission can be in the form of a planetary gearset or in the form of an arrangement of spur gear wheels.
From EP-A1 0 009 775 a range-change transmission with spur gear wheels downstream from a main transmission with two countershafts for power distribution is known. The range-change transmission has two countershafts which are rotationally independent of the countershafts of the main transmission. A floating gear wheel is arranged on the main shaft of the gearbox, which meshes with a gear wheel on each of the countershafts of the range-change transmission. This gearbox does not have sufficient capacity for absorbing axial forces that result from the gearing.
From DE-A1 196 04 824 by the present Applicant, a variable-speed gearbox with a range-change transmission of planetary design has become known. On the gearing of the planetary transmission pressure combs are provided to take up the axial forces that result from the helical gearing. The content of DE-A1 196 04 824 is intended to be fully incorporated in the present application.
The purpose of the present invention is to improve the axial mounting in a gearbox with two countershafts for power distribution.